DE3006470A1 - Coal grinding and drying installation - recirculates part of grinder waste air after dehydration to deactivate grinder atmosphere - Google Patents

Abstract

The coal dried and ground in the grinders (2) is carried out of the grinder in the stream of waste air. The pea coal is separated in a cyclone (3) and the coal dust is separated in a further cyclone (4) and is transported (13) to a silo. Part of the waste air conveyed by a fan (8) is recirculated to a hot gas generator (1) via a duct (14) and a primary air fan (7). The rest of the grinder waste air is cleaned in a filter (5). Part of the air delivered by the fan (9) is conveyed via a duct (16) to a cooler (6) with a precipitated water drain (17). Prior to its entry into the cooler part of the air is branched off and conveyed via a duct (18) to the grinder (2) as a locking air creating overpressure inside the grinder and preventing ingress of non-inert air from the outside.

Description

Method for operating a coal grinding and

drying system The invention relates to a method of operation a coal grinding and drying plant using in a hot gas generator generated hot gases, with a mill through which the hot gases flow, as well as a Separator for separating the coal dust from the mill exhaust air, with a part the mill exhaust air as return air for the purpose of inerting the mill atmosphere to the hot gas generator and / or is returned to the mill.

In the course of endeavors, especially in industries with high Energy consumption (such as in the cement industry) heating oil from coal to replace coal grinding and drying systems are becoming increasingly important. In order not to have any special guidelines for explosion protection when building and operating such systems must be observed, an inert gas operation is appropriate. Here is a extensive heating of the mill with inert gases ensures that the oxygen content 10 to 12% by volume (dry) not in the mill exhaust gas, even during the start-up and shutdown process exceeds (cf.

"Zement-Kalk-Gips", 1979, 248-253).

In a known method for operating such a coal grinder and drying system (cf.

"Zement-Kalk-Gips", 1979, 415-433, esp. Fig. 15) will some of the non-dedusted mill exhaust air is returned to the mill, and it is furthermore Part of the dedusted exhaust air (filter exhaust air) is returned to the hot gas generator. In this way, however, it cannot be sufficient in the known method Achieve inertization of the mill atmosphere.

It should be noted that if the dew point is not reached, the Mill atmosphere can lead to blockages. For this reason, the temperature must must be kept in the grinding plant at least 25 to 300C above the dew point. this so far limited the possibilities by using mill exhaust air as return air to make the mill atmosphere sufficiently inert.

The invention is therefore based on the object while avoiding this Disadvantage to train a method of the type mentioned in such a way that without exceeding it of the dew point (in compliance with the above-mentioned dew point difference) a sufficient Inerting the mill atmosphere is achieved.

This object is achieved according to the invention in that at least part of the return air before being reintroduced into the hot gas generator and / or into the mill is drained.

The water vapor contained in the mill exhaust air comes partly from the Combustion process in the hot gas generator, partly drying the coal, partly the Humidity of the ambient air. In the process that has been used up to now, the water is used exclusively withdrawn from the system with the exhaust air. The high water content of the return air is limited consequently the inertization so far with regard to the dew point difference to be observed the mill atmosphere.

In contrast, in the method according to the invention, at least one Part of the return air before it is reintroduced into the hot gas generator and / ord, ie Mill so extensively dehydrated that the dew point of the mill atmosphere is significant is lowered. The increase in the amount of return air made possible by this results in a considerable reduction in the oxygen content of the mill atmosphere and thus a perfect inerting. With the made possible by lowering the dew point Reducing the mill exhaust air temperature, the coal dust temperature is reduced at the same time, which greatly simplifies the problems associated with storing coal dust.

According to an expedient embodiment of the method according to the invention the dew point of the return air can be lowered by drainage so that a mill exhaust air temperature can be used at which a coal dust temperature of a maximum of about 650C. This allows one - otherwise for security reasons necessary - to dispense with subsequent cooling of the ground coal dust.

These and further details of the invention are the subject of the subclaims and are explained in more detail with reference to the following description of an exemplary embodiment.

The drawing shows a flow diagram of one according to the invention Process operated coal grinding and drying plant.

The system includes a hot gas generator 1, for example as a Rugel or roller mill designed mill 2, one serving to separate the grits Zyklon 3, a cyclone 4 used to separate the ground coal dust, a filter 5 designed for example as a hose or electrostatic filter, a Cooler 6, fans 7 to 10, a feed device 11 for the raw coal and a conveying device 12 for the grit to be returned from the cyclone 3 to the mill 2.

The function of the system is as follows: The one dried in mill 2 and ground coal is discharged in an air stream with the mill exhaust air.

After the grit has been separated out in cyclone 3, the coal dust is in the cyclone 4 is separated from the mill exhaust air and reaches the silo (arrow 13). Part of the Fan 8 (system fan) conveyed mill exhaust air is via a line 14 and the fan 7 (primary air fan) are returned to the hot gas generator 1. This coal dusty, unfiltered return air can be wholly or partially also via a line 15, indicated by dashed lines, between the hot gas generator 1 and Mill 2 are fed.

The remaining part of the mill exhaust air is dedusted in the filter 5. A part the filter exhaust air conveyed by the fan 9 (filter fan) is passed through a Line 16 is fed to the cooler 6 and drained here (water drain at 17). before Part of the filter exhaust air supplied via line 16 is diverted to the cooler 6 and fed to the mill 2 as sealing air via a line 18. This sealing air arrives to the gaps between the rotating and stationary parts at the inlet and Outlet of the mill and prevents the ingress of non-inert air (Fresh air), which undesirably increases the O2 content of the mill atmosphere.

The filter exhaust air dehydrated in the cooler 6 is via the fan 10 (return air fan) and a line 19 as primary air (line 19a), secondary air (Line 19b) or tertiary air (line 19c) fed back into the system. To the Line 19a can also be connected to a fresh air line 20.

In the illustrated embodiment, the line 14 and air containing coal dust is fed to the fan 7 to the hot gas generator. the at The heat generated by the combustion of the coal dust particles can either be the Cover or even cover the base load of the thermal energy required to dry the coal serve as the sole energy producer. In this way, the grinding plant becomes "self-sufficient" and only needs little or no separate energy sources.

The following comparison serves to further explain the invention between a known operating method and the method according to the invention.

1. Operational data of a known method As a known method the method according to "Zement-Kalk-Gips", 1979, p.427, Fig. 15, is selected. In the difference to the flow sheet of the present application is in the known process unfiltered mill exhaust air is fed exclusively between the hot gas generator and the mill; the filtered exhaust air reaches the hot gas generator without drainage; a sealing air is not scheduled.

Throughput 55 t / h dry coal, feed moisture 108 H20.

a) For firing: 430 Nma / h natural gas 5 860 Nm3 / h primary air (21% 02) 5 350 Nm3 / h secondary air (21% 02) 23,000 Nm3 / h tertiary air (16.5% 02r dew point 700C).

b) To the mill: 8 400 Nm3 / h false air (21% 02) 6 820 Nm3 / h water vapor 44 000 Nm3 / h non-dedusted return air Result: exhaust air in the filter 49 860 Nm3 / h temperature 950C (due to high dew point) dew point 700C 02 content 16.5% by volume (dry, i.e.

based on dry gas).

2. Operating data of the method according to the invention throughput rate 55 t / h dry coal, feed moisture 10% H20.

a) For firing: 490 Nm3 / h natural gas 6 700 Nm3 / h primary air (21% 02) 34 690 Nm3 / h secondary air (9.78% 02r dew point 450C, after water separation).

b) To the mill: 2,870 Nm3 / h false air (21% 02) 6 820 Nm3 / h water vapor 44,000 Nm3 / h non-dedusted return air (supply via line 15) Result: exhaust air in the filter 51 715 Nm3 / h temperature 85 "C dew point 560C 02 content 9.78% by volume (dry) As can be seen from the comparison, in the method according to the invention by a water vapor separation in the cleaned return air, which in the example a reduction of the dew point of the return air from 700C to 450C results in the following: - Lowering of the dew point of the mill atmosphere from 700C to 560C, - reduction of the 02 content of the mill atmosphere from 16.5% by volume to 9.78% by volume, - lowering of the Coal dust temperature from 950C to 850C.

The above example was based on the fact that the hot gas generator as primary air only fresh air, no unfiltered, carbon-dusted air Return air is supplied. With complete or partial replacement of the primary air the O2 content of the mill atmosphere can be reduced even further by means of return air.

In the illustrated and described embodiment, takes place the separation of the coal dust as well as the dedusting of the mill exhaust air by separate Aggregates. In the context of the invention, however, the operation of systems is also possible, where the separation of the coal dust and the direct dedusting of the mill exhaust air be carried out by one and the same unit. In this case, the invention is expedient part of the filtered air immediately around another part after drainage returned to the gas generator and / or mill. This is the filter Downstream filter fan used as a system fan.

In principle, hose, electric or wet filters can be used as filters Find use that are operated in negative or positive pressure.

In the illustrated and described embodiment, takes place Use a separate furnace as a hot gas generator. Is within the scope of the invention however, it is also possible, for example, to use the exhaust gases of a rotary kiln as hot gases and / or preheater.

Claims (7)

Claims: 1. A method for operating a coal grinding and drying plant using hot gases generated in a hot gas generator, with one of the hot gases flowed through the mill and a separator for separating the coal dust from the mill exhaust air, part of the mill exhaust air as return air for the purpose of inerting the mill atmosphere is returned to the lice gas generator and / or to the mill, thereby characterized in that at least a portion of the return air before being reintroduced into the hot gas generator and / or is dewatered in the mill. 2. The method according to claim 1- for operating a system containing a filter for filtering the mill exhaust air after separating the coal dust, part of the mill exhaust air after separation of the coal dust, but before filtering, is returned as unfiltered return air, characterized in that also at least part of the mill exhaust air after filtering as filtered, return air to the Hot gas generator and / or returned to the mill and this part before reintroduction is dewatered in the hot gas generator and / or in the mill. 3. The method according to claim 2, characterized in that a part the filtered return air as sealing air directly to the mill and the remaining part is returned to the hot gas generator and / or to the mill after dewatering. 4. The method according to claim 3, characterized in that the filtered and dehydrated return air as primary and / or secondary air to the hot generator and / or is supplied as tertiary air between the hot gas generator and the mill. 5. The method according to claim 2, characterized in that at least part of the unfiltered return air as primary and / or secondary air to the hot gas generator and / or is supplied as tertiary air between the hot gas generator and the mill. 6. The method according to claim 1 for operating a plant containing a filter for separating the coal dust and for direct dedusting of the mill exhaust air, characterized in that part of the filtered air immediately and another Part of the filtered air after dewatering to the hot gas generator and / or to the mill is returned. 7. The method according to claim 1, characterized in that the dew point the return air is lowered by dewatering so that a mill exhaust air temperature can be used, at which a coal dust temperature of a maximum of about 650C results.